Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To properly orient the nacelle and the rotor blades relative to the direction of the wind, wind turbines typically include one or more yaw and/or pitch bearings. The yaw and/or pitch bearings are typically slewing bearings which are rotational roller-element bearings that typically support a heavy but slow-turning or slow-oscillating load. As such, yaw bearings permit rotation of the nacelle and are mounted between the tower and the nacelle, whereas pitch bearings permit rotation of the rotor blades and are mounted between the rotatable hub and one of the rotor blades. Typical yaw and/or pitch bearings include an outer and inner race with a plurality of roller elements (e.g. ball bearings) configured between the races.
As wind turbines continue to increase in size, the slewing bearings must similarly increase in size due to increased loading. Further, in order for the slewing bearing to withstand such loading, it must include various components that can adequately react to the increased loads. Thus, for example, conventional bearings typically include spacers between each of the roller elements to maintain uniform loading throughout the bearing.
Wind turbine pitch bearings are subjected to a variety of combined loading and a variety of pitching profiles. This operational characteristic creates conditions for bearing fatigue and fretting damage, as well as ball compliment migration issues. As wind conditions in the field are random in nature, it is increasingly difficult to predict the exact movement of the rolling elements, which would give significant insight to various bearing damage modes. Further, such bearings are typically very expensive and can be difficult to access and replace. As such, failure of the bearings can result in a lengthy and expensive repair process.
If the ball movement within the bearing could be monitored, a better understanding of the causes of such movement that leads to fatigue load, fretting damage, migration issues, and/or other failure modes could also be predicted. Currently, there are no means for monitoring such movement since the balls are located within thick steel. Accordingly, systems and methods for monitoring movement of such ball bearings would be welcomed in the art as preventive maintenance could be employed before the bearing becomes damaged.